Crude oil desalting is a common emulsion breaking method where an emulsion is first intentionally formed. Water is added in an amount of approximately 5% to 10% by volume of crude. The added water is intimately mixed with the crude oil to contact the impurities therein thereby transferring these impurities into the water phase of the emulsion. The emulsion is usually resolved with the assistance of emulsion breaking chemicals, characteristically surfactants, and by the known method of providing an electrical field to polarize the water droplets. Once the emulsion is broken, the water and petroleum media form distinct phases. The water phase is separated from the petroleum phase and subsequently removed from the desalter. The petroleum phase is directed further downstream for processing through the refinery operation.
The water phase, an effluent brine, will contain the salts removed from the petroleum charge. Also present in the desalter effluent brine will be organic species. The insoluble species can be removed by traditional means (e.g., chemical flocculants), but significantly soluble species, such as benzene, still remain. Because benzene is a volatile organic carcinogen its content in wastewater is restricted by environmental regulations. Accordingly, the effluent brine typically must be treated to reduce the amount of benzene to acceptable levels for disposal. Other effluent waters include sour water stripper effluent, crude tower overhead, condensate water, crude oil and fuel tank settling draws, various petrochemical process effluent waters, or any water that has come in contact with an organic fluid where that portion of the organic fluid which has dissolved in the water must be removed.
This invention particularly applies to those organic species which are nonionic, that is, not ionizable acids or bases, and therefore relatively unaffected by pH, but are polar enough to have significant solubility in water. Species such as these which are also relatively volatile and/or carcinogenic, such as benzene, are of particular concern.
The present inventor discovered that appropriate treatments of effluent water can desolubilize the benzene and increase the amount removed by traditional techniques, such as extraction, stripping, and distillation.